The present invention is directed generally to detonators, and more particularly, to an electronic detonator such as is used in electronic blasting systems, having a pre-fire countdown.
Prior art electronic blasting systems include a final countdown that commences automatically upon insertion or upon powering up of the bus. For example, U.S. Pat. No. 4,712,477, entitled “Electronic Delay Detonator” and issued to Aikou et al., describes the use of a RC charging circuit to trigger the electronic detonator upon power-up. Once the firing sequence is initiated in such systems, however, there is no period of time allowed during which it can be aborted if appropriate.
Further, in such systems, if a specific detonator does not power properly or there is a power glitch in the bus, the firing sequence will be reset or not initiated properly. And once the firing sequence is initiated, detonation will commence even if there is a fault condition in one or more detonators, possibly resulting in a less successful blast. This potential problem can be significant where there is environmental noise (ESD, RFI, EMI, etc.) in the system.